Sporadic, Intermittent Whining Noise When shifting from Reverse to Driv

[Jack Benny]

I have a 2008 Mercury Mountaineer. It has 80,000 miles on it and has been well maintained and is overall in great shape. For a while now, there has been a random noise happening. It only happens when I have backed out of my driveway or a parking spot. Normally when it occurs, I had turned my steering wheel a lot in the backing out and once I switched to drive and started moving forward, there would be a whining noise for a few seconds. No other symptoms felt or heard in the car. This only happened sporadically, sometimes going months without it and sometimes a few times a week. I thought it was the power steering even though I had no issues actually turning the wheel, etc. I had that all checked out and it was fine. I even had my last regular maintenance last week and everything looked fine. Then on Saturday, I was in a parking lot and I reversed straight back to get a spot. When I put the car back in drive the whine occurred but I had not touched the steering wheel. I needed up backing up again a moment later and the same thing took place when I switched to drive. No other symptoms felt or heard. I haven't been able to reproduce the sound since and neither has my Ford dealer service department. I'm just trying to see what else this could be. Has anyone had an issue like this? Any advice would be greatly appreciated.

Thanks,